1. Field of the Invention
The present invention relates to an image detecting device, and in particular, to an image detecting device that detects an image by using a substrate at which are provided protection lines for discharging static electricity that is generated at the time when the substrate is manufactured.
2. Description of the Related Art
Radiation image detecting devices, such as FPDs (flat panel detectors) and the like in which an X-ray sensitive layer is disposed on a TFT (thin film transistor) active matrix substrate and which can convert X-ray information directly into digital data, have been put into practice in recent years. As compared with a conventional imaging plate, an FPD has the advantages that an image can be confirmed immediately and that moving images as well can be confirmed, and the popularization of FPDs has advanced rapidly.
In this type of radiation image detecting device, it is important to detect an X-ray image at a size that projects a human body, and therefore, substrates of large sizes exceeding 30×30 cm are needed. However, it is difficult to manufacture a substrate of such a large size from a silicon substrate. Therefore, currently, TFT active matrix substrates that are formed on a thin plate glass are mainly being used.
TFT active matrix substrates are employed as driving substrates for LCDs (liquid crystal displays), and are stable technologically and in terms of cost as well. Therefore, TFT array substrates for image detecting devices as well are mainly manufactured on assembly lines for TFTs for LCDs from the standpoint of cost.
A circuit diagram of a conventional TFT active matrix substrate 10′ for an image detecting device is shown in FIG. 6.
As shown in FIG. 6, the TFT active matrix substrate 10′ is structured such that a large number of pixels are arrayed in a two-dimensional form. The pixel is structured to include a charge collecting electrode 11′ that collects charges generated at an unillustrated image sensor portion, a charge accumulating capacitor 5′ accumulating detected charge signals, and a thin film transistor (hereinafter called “TFT switch”) 4′ for reading out the charges accumulated in the charge accumulating capacitor 5′. Further, plural scan lines (gate lines) 101′ for turning the TFT switches 4′ on and off, and plural data lines 3′ for removing the charges accumulated in the charge accumulating capacitors 5′, are provided at the TFT active matrix substrate 10′. One electrode of the charge accumulating capacitor 5′ is grounded via an unillustrated line and is ground level. Note that, in FIG. 6, the one electrode of the charge accumulating capacitor 5′ is illustrated as being connected to ground.
The respective data lines 3′ and the respective scan lines 101′ of the TFT active matrix substrate 10′ are connected to a common line 110′ via bidirectional diodes 30′ for circuit protection respectively, in order to prevent electrostatic breakage at the time of manufacturing.
An example of the structure of one diode 31′ that structures this conventional bidirectional diode 30′ is shown in FIG. 7.
In a TFT active matrix substrate that uses an amorphous silicon TFT, the diode 31′ can be structured easily by connecting the gate electrode and the drain electrode of the TFT switch, as shown in FIG. 7.
FIG. 8 is shown as an equivalent circuit focusing on one TFT element of the TFT active matrix substrate 10′ shown in FIG. 6.
As shown in FIG. 8, at each TFT element of the TFT active matrix substrate 10′, between the gate electrode of the TFT switch 4′ and the data line 3′ is equivalent to being connected by the bidirectional diode 30′ that is structured by the anodes and cathodes of two of the diodes 31′ respectively being connected to one another in parallel. Therefore, if the electrode potential of one becomes high, charges flow to the other, and the potential can be prevented from becoming high.
The problem of static electricity, in a case in which such a TFT active matrix substrate is manufactured by using a TFT assembly line for LCDs, is described next with reference to FIG. 9A through 9E.
The size of the substrate that can be manufactured on an assembly line for TFTs for LCDs depends on the device size of the assembly line, and is a size peculiar to that line. Currently, large substrates of mainly about 1 m2 can be manufactured.
In a case of using a TFT assembly line for LCDs that can manufacture such large-sized substrates, a TFT array substrate 10B′, at which a single or plural TFT array cells 10A′ for FPDs are formed, is manufactured (see FIG. 9A).
The manufactured TFT array substrate 10B′ is divided in primary dividing process, and the TFT array cells 10A′ are cut out (see FIG. 9B). In a sensor layer forming step that is carried out after, layer formation is carried out mainly by vacuum deposition or CVD (chemical vapor deposition), and therefore, the device cost-increases in proportion to the substrate size. Accordingly, in the primary dividing process, it is desirable to cut the TFT array cells 10A′ out from the TFT array substrate 10B′ at the minimum size needed as the TFT array cells 10A′, and make the chamber size of the manufacturing facility smaller.
Next, sensor layer formation and upper electrode formation are carried out on the cut out TFT array cell 10A′. After formation is completed, a sealing process that covers the sensor layer and the upper electrodes with a glass substrate or resin or the like is carried out (see FIG. 9C).
Subsequently, the TFT array cell 10A′ after the sealing process is subjected to secondary dividing. Up until this secondary dividing process, a short ring 120′ is provided at the TFT array cell 10A′ in order to protect the gate insulating films of TFT switches 4′. In this secondary dividing, the short ring 120′ is separated from the TFT array cell 10A′ and the respective terminals are electrically and physically separated (see FIG. 9D), in order to carry out TCP packaging in the next process.
Next, packaging of gate drivers and amp ICs (the packaging of ICs that are packaged on a TCP (tape carrier package)) is carried out on the TFT array cell 10A′ from which the short ring 120′ has been separated. Finally, the circuit substrates (a gate drive substrate, a signal detecting circuit substrate, and the like) are packaged, and the TFT active matrix substrate 10′ is completed (see FIG. 9E).
Here, the short ring 120′ is a line that connects the electrodes of the both ends of the insulating film in order to prevent application of voltage to the insulating film.
Namely, at the case of the above-described TFT array cell 10A′, the final end portions of the data lines 3′ and the scan lines 101′ are connected by a metal line that is disposed at the peripheral edge of the array. Due thereto, even in a case in which charges are given to a given data line 3′ due to static electricity or the like and the potential becomes high, the charges flow out immediately to the short ring 120′, and voltage is thereby prevented from being applied to the insulating film.
Conversely, in a case in which there is no short ring 120′ at the TFT array cell 10A′, it is often the case that a strong electric field is applied to the insulating film due to static electricity, and due thereto, shifting of the characteristic of the TFT or dielectric breakdown (a leak defect) arises.
By providing the short ring 120′ at the TFT array substrate 10B′ in this way, the manufacturing yield of the TFT array cells 10A′ can be maintained high, and therefore, the manufacturing cost can be kept low.
On the other hand, as shown in FIG. 9E, from after the secondary dividing up to the TCP packaging and circuit packaging, the input and output terminals of the TFT array cell 10A′ are in completely electrically separated states. Therefore, because this is the same as a case in which there is no short ring 120′, there is the concern that a shift in the characteristic or a dielectric breakdown defect will arise.
In order to prevent this, as shown in FIG. 6, it is usually the case that the bidirectional diodes 30′ for protection are disposed between the respective data lines 3′ and a common line 110′ that is disposed at the peripheral edge of the active matrix array. Due thereto, charges can flow to the adjacent lines and electrostatic defects can be suppressed, although not to the extent as when the short ring 120′ is used.
As a related art, Japanese Patent Application Laid-Open No. 10-177186 discloses a structure as follows: in a case in which a TFT active matrix substrate is used as the driving substrate of an LCD, a common line is formed so as to surround the display region. Bidirectional diodes for protection are formed between the common line and the respective data lines. Even in cases in which static electricity flies into the respective data lines, the static electricity is dispersed to the common line via the respective bidirectional diodes, and the TFT is thereby protected.
In a voltage controlling type device such as the LCD shown in Japanese Patent Application Laid-Open No. 10-177186, even when the common line 110′ is formed and the bidirectional diodes 30′ are inserted between the common line 110′ and the respective data lines 3′ and respective scan lines 101′ as described above, there is no problem at all as an applied product. This is because an LCD is a voltage controlling type device that controls the voltages that are applied to the respective data lines 3′ and the respective scan lines 101′ of the TFT active matrix substrate.
Namely, in a case in which a potential difference arises between the respective data lines 3′ at the time of actual driving, current flows via the bidirectional diodes 30′. However, the potentials of the respective data lines 3′ are maintained because the resistance values of respective diodes 31′ are sufficiently high with respect to the data lines 3′. Therefore, this structure is not an impediment in any way in an LCD in which the driving conditions are determined by voltage.
On the other hand, in an FPD as well, no problems arise with respect to the driving of the respective scan lines 101′, in the same way as in an LCD. However, the data line 3′ sides are signal detecting circuits (amp circuits) that detect charge amounts. Therefore, if, at the time of actual driving, a potential difference arises between the respective data lines 3′ and leak current flows between the data lines, there is the problem that the signal values of the data lines, that are detected at a signal detecting circuit, fluctuate. Due thereto, there is the problem that false data information enters into the other data lines 3′ and artifacts (false images) appear.